1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to solid golf balls having a core, a mid layer and a cover.
2. Description of the Related Art
Golf balls have numerous dimples on the surface thereof. In general, golf balls have single radius dimples having a cross-sectional shape with single curvature radius, or double radius dimples having a cross-sectional shape with two curvature radii. The dimples disrupt the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separating points of the air from the golf ball shift backwards leading to the reduction of a drag. The turbulent flow separation promotes the difference between the separating point on the upper side and the separating point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. Such a role of the dimples is referred to as a “dimple effect”. Excellent dimples disturb the air flow more efficiently.
A variety of proposals with respect to the dimples in attempts to improve flight performances have been made. JP-A No. H05-96026 (U.S. Pat. No. 5,338,039) discloses dimples having a shape with the gradient of a slope disposed in the vicinity of the edge being greater than that of a slope at the bottom part. JP-A No. H09-70449 (U.S. Pat. No. 5,735,757) discloses dimples having a cross-sectional shape given by double radius. JP-A No. 2004-166725 (U.S. Pat. No. 6,899,643) discloses dimples having a great ratio of the curvature radius of the bottom part to the curvature radius in the vicinity of the edge.
For golf balls, in addition to flight performances, control performances are also important. Control performances correlate to spin performances. Great back spin rate results in small run (i.e., distance from point of fall of the golf ball to the point where it stopped). For golf players, golf balls which are liable to be spun backwards are apt to be rendered to stop at a targeted position. Great side spin rate results in easily curved trajectory of the golf ball. For golf players, golf balls which are liable to be spun sidewise are apt to allow their trajectory to curve intentionally. High-level golf players particularly place great importance on control performances upon iron shots. Soft covers are responsible for control performances. JP-A No. H09-239068 (U.S. Pat. No. 5,782,707) and JP-A No. H10-151226 (U.S. Pat. No. 5,899,822) disclose a golf ball having a soft cover.
Combinations of a soft cover and unique dimples have been also proposed. JP-A No. 2001-54588 (U.S. Pat. No. 6,702,695) discloses a golf ball having a soft cover, and having dimples improved with respect to their volume. JP-A No. 2002-355342 (U.S. Pat. No. 6,620,059) discloses a golf ball having a soft cover, and having dimples improved with respect to their contour length.
When the golf ball in which a soft cover is used is hit with a driver (W#1), hopping of the golf ball may be caused due to excessive spin. Thus hopped golf ball may not achieve sufficient flight distance.
When golf balls are hit with a short iron, the surface thereof may be scuffed. Particularly, in the case of golf balls having double radius dimples, peripheral edges are liable to be scuffed resulting from concentration of stress. There is still room for improvement of dimples with respect to the scuff resistance.
An object of the present invention is to provide a golf ball that is excellent in the control performance, flight performance and scuff resistance performance.